Physiological role of gonadotropin-releasing hormone (LH-RH) on ovarian function ; phosphoinositide metabolism in granulosa cells.

在大鼠颗粒细胞中，LH-RH以剂量依赖性方式诱导三磷酸肌醇（IP <D23>D2）形成。LH-RH可抑制促卵泡激素（FSH）刺激的雌激素分泌，并与LH-RH刺激的IP_3形成平行。两种现象的半数最大效应发生在约10 μ <-9>M LH-RH。刺激IP_3形成和抑制雌激素产生的镜像数据可能表明颗粒细胞中刺激的磷酸肌醇降解与抑制的类固醇合成紧密耦合。芳香化酶活性被认为是颗粒细胞中雌激素形成的限速步骤，以雄烯二酮向雌酮的细胞转化率来测量。FSH对芳香化酶活性有明显的抑制作用，滞后时间为32 h。FSH对雌酮产生的影响在前32 h内不明显，此后雌酮产生速率逐渐增加。与LH-RH同时孵育降低 ...更多信息 将FSH诱导的雌酮产生降至对照水平。FSH刺激雌酮产生的50%有效浓度（EC_（1<50>））在有或无LH-RH的细胞中几乎相等，表明FSH对雌酮产生的抑制方式为非竞争性抑制。用蛋白激酶C激活剂测得的LH-RH数据完全一致。蛋白激酶C的激活可能抑制FSH诱导的芳香化酶的诱导，然后进行，以确定是否持久的受体占用是必要的LH-RH对颗粒细胞发挥这种作用，或是否LH-RH的作用继续由第一次和短暂的刺激LH-RH，使用竞争性拮抗剂antide。LH-RH刺激磷酸<32>参入磷脂酰肌醇（PtdIns），这种参入可以通过用反式肽取代先前结合的LH-RH而终止，并通过用LH-RH重新占据受体而重新开始。Antide可迅速阻止LH-RH刺激的Ptdlns磷酸化。在LH-RH的抗FSH作用中也观察到antide的相同作用。FSH启动的芳香化酶活性被LH-RH淬灭，当LH-RH被antide从其受体上去除时，芳香化酶活性重新开始。这两个反应与LH-RH受体的占用提供了证据，有利于刺激Ptdlns周转抑制芳香化酶激活的紧密耦合。这些数据需要芳香化酶的持续激活。综合这些数据，需要持续占用受体的LH-RH发挥其作用，LH-RH或LH-RH样激素在卵巢，除了从垂体，可以参与控制类固醇激素在卵巢中的自分泌或旁分泌的方式。少

In rat granulosa cells, LH-RH induced inositol trisphosphate (IP<D23>D2) formation in a dose-dependent manner. Estrogen production in response to follicular-stimulating hormone (FSH) was reduced by LH-RH in parallel with LH-RH-stimulated IP_3 formation. Half maximal effects of both phenomena occurred at about 10^<-9> M LH-RH. The mirror-image data of stimulation of IP_3 formation and inhibition of estrogen production might suggest tight coupling of stimulated phosphoinositide degradation to suppressed steroidogenesis in the granulosa cells. The aromatase activity, considered as rate-limiting step of estrogen formation in granulosa cells, was measured as the rate of cellular conversion of androstenedione to estrone. FSH exerted a markedly inhibitory effect on the aromatase activity with a lag time of 32h. There were slight effects of FSH on estrone production for the fust 32h, and, thereafter, the rate of estrone production increased progressively. Concurrent incubation with LH-RH decre … More ased the FSH-induced estrone production to the control level. The 50% effective concentration (EC_<50>) for FSH stimulation of estrone production was almost equal in the cells incubated with or without LH-RH, suggesting the noncompetitive inhibitory fashion. The identical data of LH-RH was obtained by protein kinase C activators. Protein kinase C activation might inhibit FSH-induced aromatase induction.It was then undertaken to determine whether persistent receptor occupancy was necessary for LH-RH to exert such actions on granulosa cells, or whether LH-RH actions were continued by a first and transient stimulation by LH-RH, using a competitive antagonist, antide. LH-RH stimulated[ ^<32>Plphosphate incorporation into phosphatidylinositol (PtdIns), which could be terminated by displacement of previously bound LH-RH from its receptor by antide and restarted by reoccupying the receptors with LH-RH. Antide could rapidly prevent LH-RH-stimulated Ptdlns phosphorylation whenever it was added to incubations. An identical effect of antide was observed also in the anti-FSH action of LH-RH. The aromatase activity initiated by FSH was quenched by LH-RH and restarted at a time when LH-RH was removed from its receptor by antide. These two responses associated with the occupancy of LH-RH receptor provide the evidence in favor of a tight coupling of stimulated Ptdlns turnover to suppression of aromatase activation. These data of required continued activation of aromatase activation. Taken together these data of requirement of continued occupancy of receptor for LH-RH to exert its action, LH-RH or LH-RH-like hormone in ovaries, in addition to from pituitary, could participate in the control of steroidogenesis in the ovary in an autocrine or a paracrine manner. Less